The present invention is in the general field of packaging of fiber optics, and is in particular a package that maintains precise alignment and spatial placements of the optical fibers.
Fiber optics is a rapidly evolving field. The basic optical fiber concept capitalizes on the intrinsic low loss and high speed data transmission of the fiber. The use of fiber optics has created a whole burgeoning industry. Optical fibers are used in various telecommunication and network applications, as reviewed by C. Yeh, "Handbook of Fiber Optics; Theory and Applications", (Academic Press, San Diego, Calif., 1990), and H. Murata, "Handbook of Optical Fibers and Cables" (Marcek Dekker, New York, 1988). In the foreseeable future, the field is expected to experience a quantum leap in stature and product diversification. Anchoring such development is the recent advances in fiber coupling technologies.
The very fact optical fibers are low loss media implies difficulties in coupling and distributing signals among multiple fibers. To date, fiber coupling can be achieved by several means. The major classes are fused biconic taper and planar waveguides, as described by K. Murphy, Lasers and Optronics, 10:5, 63 (1991). Also significant are beam splitter taps employing angled mirrors, half mirrors or spherical mirrors (or lenses).
When two dissimilar materials are joined together and subjected to heat or cool cycles, the differences in their thermal expansion coefficients can induce large stresses. Depending on the exact geometry and material distribution, the transient stress field may be quite complex. Stress concentration points may easily damage fragile microstructures. Even in a simple layout such as two thin fibers adhering to each other, temperature cycling may cause the bi-material strip to curl and flex, accelerating fatigue of the system.
Since the traditional packaging approach is to employ a plastic-based encapsulant (e.g., epoxy) to wrap the bare device, transient stresses pose a significant device reliability problem. The plastic encapsulant is sometimes filled with solid particles in order to approximate the thermal expansion properties of the substrate (device). However, an exact match is not possible, especially over a wide service temperature range. The traditional encapsulants also arguably do not form strong chemical bonds with the substrate, permitting potential delamination at material interfaces during stress cycling. Moisture and/or chemical ingression along delaminated interfaces further deteriorates coupler performance. When the encapsulants are unevenly distributed over the packaged devices, stress concentration point, shear, compression, tension, and torque movements can all be expected in a complex coupler.
In addition to transient stresses accompanying temperature cycling, stress often exists in as-packaged devices without temperature cycling. This phenomenon is due to the shrinkage associated with polymerization (curing) of encapsulants. Since the packaging material and the substrate are both in the glassy states under normal use conditions, shrinkage of a polymeric material as it is formed around a device may engender appreciable stress.
It is therefore an object of the present invention to provide an improved method for making optical fiber couplers.
It is a further object of the present invention to provide packaged optical fiber couplers having decreased shrinkage.
It is also an object of the present invention to provide an improved method for making, and packaging, for fiberoptics transceivers.